Method for design and manufacturing of optics for holographic sight

ABSTRACT

A method for design and fabrication of holographic optical elements for a compact holographic sight is proposed. The method includes use of ray-trace software to design holographic elements having optical power using an intermediate hologram with parameters obtained through minimization of the merit function defining image quality.

BACKGROUND OF THE INVENTION

See-through optical sights for simulation, training, and close combat(distances less than ˜1000 m) based on collimated optics have been inuse for years.[1—Elementary optics and applications to fire controlinstruments: May, 1921 By United States. Army. Ordnance Dept, page 84,2—R. P. Grauslys, A. R. Harding, ‘Weapon Aiming Device’, U.S. Pat. No.7,530,192 B2 (2009)]. The advantage of collimated optics based sights isin the reticle image appearing in the same plane or close to the targetplane. This makes the targeting more precise and comfortable. Usually, asee-through monocular optical sight consists of a reticle illuminatedwith some small light source, reflective and/or refractive optics tocreate a magnified virtual image of the reticle for a viewer's eye. Thesimplest type of reticle is a “red dot”—just an LED or laser diode as areticle. The disadvantage of regular see-through sight optics is in lowlight throughput due to the unavoidable losses of semitransparent opticsfor both see-through and reticle image. Implementing narrowbandreflecting dichroic mirrors mitigates this problem, but requires narrowbandwidth laser diodes. Implementing laser diodes in sights isquestionable as accumulated exposure to bright laser light/scatter inthe visible spectrum range can bring to damage of the shooter's eye.Speckled reticle image is also an issue.

Holographic optics based sights implementing high efficient (>90%) thickholograms have higher light throughput [3—R. Bhatt, ‘Testing ofHolographic Optical Elements for Holographic Gun-Sight’, Optics andLasers in Engineering, Vol. 46, pp. 217-221 (2008), 4—W. R.Houde-Walter, ‘Head up Display for Firearms”, U.S. Pat. No. 7,721,481 B2(2010)]. The deficiency of existent holographic sights is inimplementing laser diodes to avoid dispersion and in rather complicatedmulti-element optics needed to compensate aberrations [5—A. M. Tai, E.Sieczka, ‘Lightweight Holographic Sight’, U.S. Pat. No. 6,490,060 B1(2002), Assignee EOTech Inc.]. This sight optics, with the reticle imagerecorded in the hologram, requires individual time consuming alignmentof each element, and applied laser diode creates the coherent reticleimage with significant speckle that is negatively affecting the imageperception.

An edge-illuminated substrate holographic approach with a singlehologram for see-through reticle image creation was proposed [6—J.Upatnieks, ‘Compact Holographic Sight’, Proc. SPIE, Vol. 883, pp.171-176 (1988)]. Such approach indeed allowed for a see-through imagerywith simultaneous view of the outside world, however the image qualitywas rather poor for a broad-band light source, mostly because of thecolor dispersion created by a single hologram for a broad-band source;for a laser-based (narrow-band) source, an unwanted shift in virtualimage position was observed with a drift in laser diode wavelength dueto, e.g., external temperature changes. A single-hologram approach wasfollowed by some developers [7—Simmonds, 8—Takeyama, 9—Kasai] forcompact see-through head (helmet)-mounted displays (HMDs) using either asingle laser source for object illumination or proposing verycomplicated hologram recording geometries for generating asphericrecording wave-fronts which are rather complicated and costly to beimplemented in practice. While providing substantially much morefield-of-view that is actually required, e.g., for a see-through weaponsight, it is understood in the art that these developed designs, with areduced field-of-view and an extended eye-relief, can be used assee-through sights with an illuminated (or, holographically-recorded)reticle replacing a micro-display required as image source for HMDs.

Another approach uses diffractive elements placed on a transparentwaveguide to create an enlarged see-through virtual image for a viewer[10—P. Repetto, E. Borello, S. Bernard, ‘Light Guide for Display Devicesof the Head-Mounted or Head-up Type, U.S. Pat. No. 6,825,987 B2 (2004),11—T. Levola, Method and Optical System for Coupling Light Into aWaveguide, U.S. Pat. No. 7,181,108 B2 (2007)]. While providing asee-through capability, such approach suffers from stray light generatedby unwanted diffraction into undesired diffractive orders thatsubstantially decreases the image quality and contrast.

Another approach uses partially reflective elements placed at some angleon a transparent waveguide [12—Ya. Amitai, ‘Substrate-Guided OpticalBeam Expander’, U.S. Pat. No. 6,829,095 B2 (2004)]. While creating asee-through imagery, fabrication of such elements in mass quantities canbe prohibitively expensive, and providing a needed long eye-relief (˜100mm) is not possible.

In an attempt to remove the color dispersion/shift of the imagery,another approach was introduced that uses two substrate-guided coupledholograms for a see-through image creation [13—Ya. Amitai, A. Friesem,I. Shariv, ‘Planar Holographic Optical Device for Beam Expansion andDisplay’, U.S. Pat. No. 6,169,613 B1 (2001), 14—F. Dimov et al.,‘Holographic Substrate-Guided Wave-Based See-Through Display’, US2010/0157400 A1 (2010), 15—H. Mukawa, ‘Optical Device and Virtual ImageDisplay’, U.S. Pat. No. 7,453,612 (2008), 16—H. Mukawa, K. Akutsu,‘Optical Device and Virtual Image Display Device’, U.S. Pat. No.7,418,170 (2008), 17—Y-R. Song, ‘Wearable Display System AdjustingMagnification of an Image’, US Pat. Application US2004/0004767 A1(2004)]. The two holograms are coupled through a common substrate due toTIR. The chromatic dispersion of the first hologram is corrected by thedispersion of the second one, and the design is insensitive to lightsource wavelength drift/shift. While providing a means to mostly removethe color dispersion/shift from the imagery for the case when twoidentical holographic gratings are placed mirror-symmetrically on thewaveguide, the developed systems require incorporation of additionaloptics that adds up to weight, volume, and cost. A desired reduction ofthe number of optical elements for such see-through systems was notclarified, except for [13—Ya. Amitai, A. Friesem, I. Shariv, ‘PlanarHolographic Optical Device for Beam Expansion and Display’, U.S. Pat.No. 6,169,613 B1 (2001)], where a compact sight was proposed thatincorporates a holographic lens coupled to a holographic grating throughthe total internal reflection (TIR) in the substrate. While indeedshowing a good image quality for up to 4.0 mm diameter Eye Box size, thedemonstrated Eye Box size is not large enough to provide an adequatesee-through sight.

In the last ten years, software-based ray-trace techniques of designingholographic elements substantially advanced compared to traditionalmulti-step recursive analytical techniques described in, e.g. [13—Ya.Amitai, A. Friesem, I. Shariv, ‘Planar Holographic Optical Device forBeam Expansion and Display’, U.S. Pat. No. 6,169,613 B1 (2001)]. Usingcommercial off-the-shelf software such as, e.g., Zemax® or Code V®, itis quite possible to implement, in a robust and re-producible way,rather sophisticated holographic designs, thus revealing essentially newfeatures in multi-component holographic systems. An additional advantageof such an approach compared to a traditional analytical recursive oneis that it is rather straightforward to transfer a software-made designon an optical table and, actually, implement recording in practice.

What is desired is a method to design and fabricate substrate-guidedholographic optical elements for a compact see-through weapon sight,which is reliable, reproducible, capable of providing large enoughaperture sizes (e.g., up to 1.5 inch diameter), and extendable forlow-cost mass production. In such a sight, in a compact form-factor,there is a thin transparent waveguide with holographic elements enablingin-coupling and out-coupling of light to/from the waveguide in such away as to create a sufficient field-of-view, aberration-free virtualimage of the reticle superimposed on the scene view, with a capabilityto provide a long (up to 100-200 mm) eye relief, and to provide ahighly-transparent (˜90%) view of the outside world, with parallaxreduced to unnoticeable, for a shooter level. At the same time, amonocular sight provides a see-through imagery without introduction ofany noticeable color shifts/changes and laser speckle in thefield-of-view and should be safe for a shooter's eye, and thereforeavoid using laser illumination. The compact optical sight describedabove is the concept described in [13—Ya. Amitai, A. Friesem, I. Shariv,‘Planar Holographic Optical Device for Beam Expansion and Display’, U.S.Pat. No. 6,169,613 B1 (2001)]. As was shown in [14—F. Dimov et al.,‘Holographic Substrate-Guided Wave-Based See-Through Display’, US2010/0157400 A1 (2010)], such a system can be made of substantialaperture sizes (e.g., ˜1.5 inch diameter). It requires a broadbandillumination source, provides a see-through imagery without color shift.

SUMMARY OF THE INVENTION

A substrate-guided holographic sight as an efficient weapon aimingsolution for close combat (up to 1000 m), such as for a projectileweapon, comprises the subject invention. It is based on advancedholographic techniques, and has a single-component optical elementcomprising a light-guide plate, two coupled holographic optical elementspaired with a thin transparent plate with a reticle, and a miniature LEDmodule with a diffuser for reticle illumination. Divergent light fromthe LED module illuminates the reticle on the transparent plate. Theimage of the reticle is formed by a substrate-guided holographic lenscoupled to a substrate-guided holographic grating through TIR in thesubstrate-guided holographic sight substrate. Diffusive illuminationsupports uniform image brightness across the entire 1.5 inches eyebox. Ashooter aims a weapon through the transparent holographic grating partof the substrate-guided holographic sight.

Another aspect of the disclosure provides a method of design andrecording holographic optical elements for substrate-guided holographicsight using an intermediate hologram and a ray-tracing technique thatincludes optimization of image quality using a damped-least squareoptimization procedure for the merit function minimization.

The benefits and advantages of the disclosure will be apparent to thoseskilled in the art from the discussion that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of optical portions of one operativesubstrate-guided holographic sight;

FIG. 2 is a ray-trace design of substrate-guided holographic sight,holographic lens 214 is recorded using a collimated wavefront and adivergent spherical wavefront, wavelengths: 0.532 μm, 0.525 μM, 0.510μm;

FIG. 3 is a ray-trace design of a holographic sight usingtransmissive-type holographic elements.

FIG. 4 is a ray-trace design of a holographic sight using reflectivetype holographic elements.

FIG. 5 is a spot diagram showing image quality for the ray-trace designof FIG. 2, fields-of-view are: 0 deg, −0.6 deg, +0.6 deg, wavelengths:0.532 μm, 0.525 μm, 0.510 μm;

FIG. 6 is a collimated wavefront used in recording holographic lens 214;

FIG. 7 is a ray-trace for recording holographic lens 214 using anintermediate hologram; and

FIG. 8 is a spot diagram showing image quality for the ray-trace designof FIGS. 4 and 5, fields-of-view are: 0 deg, −0.6 deg, +0.6 deg,wavelengths: 0.532 μm, 0.525 μm, 0.510 μm.

FIG. 9 is a ray-trace design showing use of a micro display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, unless otherwise stated, the term recorded orrecording refers to the fabrication of a holographic element.

Although the present invention is susceptible of embodiment in variousforms, there is shown in the drawings and will hereinafter be describedpresently preferred embodiments with the understanding that the presentdisclosure is to be considered as an exemplification of the inventionand is not intended to limit the invention to specific embodimentsillustrated.

It is to be further understood that the title of this section of thespecification, namely, “Detailed Description of the PreferredEmbodiments” relates to a rule of the United States Patent and TrademarkOffice, and is not intended to, does not imply, nor should be inferredto, limit the subject matter disclosed herein or the scope of theinvention.

The method of the subject invention comprises a design for the optics ofa see-through holographic weapon sight, with the optical parameterscomparable to optical sight based on common optics, with performance interms of brightness (luminance), contrast, absence of speckle andscattered light that degrades the reticle image, absence of parallax,the number of components used, weight, and cost in a manner that exceedspresent optical sights that are based on optics common in the art.

Referring to FIG. 1, a substrate-guided holographic sight 110 of thesubject invention has a first hologram 112 and a second hologram 114either laminated directly to a substrate 116 or, alternatively,laminated onto thin (˜1 mm) substrates 113 that are attached to thesubstrate 116. The substrates 113 and 116 are substantially transparentin at least a portion thereof, but may be also entirely transparent inthe visible spectrum range (400 nm-700 nm). The substrate 116, or plate,can be made from a number of materials. For example, the transparentportions of the plate 116 can be made of glass, polycarbonate plastic oracrylic plastic. Such a plate 116 is at least operative when having athickness of the 3-6 mm, but can also be operative at other thicknesses.The external surface of the plate 116 should have a first transparentregion 118 (from the reticle side only, the other side can be opaque inthe first region) for accepting a transmitted image of the reticle, asecond transparent region 120 for transmitting the accepted image, and athird viewing region 122 that permits viewing through the entire plate,and a transparent volume 124 throughout the substrate along with theentire path from where the transmitted image is accepted to where theaccepted image is transmitted. All of the transparent regions mayoverlap with each other, and the substrate is not restricted from havingtransparent regions or volumes that are larger than mentioned.Substrates 113 can be made from, e.g., optical quality soda-lime glasssuch as the glass used for manufacturing liquid crystal displays andsupplied, e.g., by Corning, and attached to the substrate 116 using aUV-curable optical glue manufactured, e.g., by Norland Products.Alternatively, they can be made of optical quality plastic materialknown in the art.

The substrate 116 is depicted in the figures as a single, unitary bodyof a single material. However, the substrate 116 may also comprise aplurality of bodies made of a single or a plurality of materials. Aperson of ordinary skill in the art will be capable of using ray-tracingsoftware to determine whether the particular configuration of materialsand bodies will serve to transmit the accepted image to where it can betransmitted to a viewer.

The substrate 116 as depicted is an uncoated unitary body. As such, theaccepted image is conveyed to the region 120 where the image istransmitted out of the substrate 116. This conveyance may be donedirectly, without internal reflections by the accepted image beingconveyed to the transmission area in a straight line. This conveyancemay also be done by internal reflections. One way to achieve internalreflection is to coat the substrate at the locations where reflection isrequired with a reflective material, many of which are known to those ofordinary skill in the art. An evaporated layer of silver is an exampleof a coating 126, although the reflective layer may be applied by anymeans and may be of any composition that is functional.

Another way to achieve internal reflection is by total internalreflection (TIR). In this case, the substrate must either have an indexof refraction, relative to the environmental medium, sufficient tointernally reflect the light of the accepted image. Total internalreflection is especially preferred for reflections that occur near theportion of the substrate 116 where the accepted image is transmitted outof the substrate 116. For example, for an air-acrylic interface,α^(TIR)=sin⁻¹(1/1.49)=42.2°.

Transparent means that the substrate 116 is capable of permitting lightthrough to allow a shooter to receive and interpret the image of thereticle and to see the target. Accordingly, the substrate 116 may betinted or have other modifications that do not render the deviceinoperative. For example, any material will have some amount ofdiffusion from imperfections or inclusions, but the diffusion should notbe so great as to prevent the acceptance, conveyance, and transmissionof the image by the substrate 116.

Referring further to FIG. 1, the first transparent region 118 (acceptinga transmitted image) faces first hologram H1 112; the second transparentregion 120 (transmitting the accepted image) faces second hologram H2114; the third transparent region is at least as large as the field ofview 128 and includes the surfaces on both sides of the substrate andthe volume in between.

The first and second holograms 112 and 114 can be placed either on thesame side of the substrate, or on opposite sides. Holograms H1 and H2 infact are holographic optical elements (HOE), either or both of them canhave optical power. The preferred embodiment has at least one withoptical power.

In one embodiment, first hologram H1 112 has optical power. As such,first hologram H1 112 is a holographic lens. In that embodiment, secondhologram H2 is a holographic grating 112 with no optical power.

A distinctive feature of these holograms is their capability to couplethe light in the substrate at angles larger than or equal to totalinternal reflection (TIR) angle of the substrate, and to out-couple thelight that propagates along the substrate.

Another distinctive feature of these holograms 112, 114 is that they areBragg holograms. This means that they diffract the light in singlediffraction order. Hence their diffraction efficiency can be very high(theoretically 100%). This results in very high light throughput of theoptical system. Contrary to this, other see-through sights are based onbeam combiners (semitransparent or dichroic mirrors) and have muchsmaller light throughput.

Another distinctive feature of holograms 112, 114 is that they arerecorded with lasers of, e.g., three different colors (e.g., Blue at 457nm, Green at 532 nm and Red at 647 nm), thus providing a means ofgenerating an image of the reticle in either color, depending onshooter's preference and the color and tint of the background scene.

The substrate-guided holographic see-through sight 110 operates by usingsubstrate-guided wave (SGW) holograms. Some basic information about SGWholograms and theory developed is presented in H. Qiang and J. A.Gilbert, “Diffraction Properties of Substrate Guided Wave Holograms”,Optical Engineering, col. 34, no. 10, p. 2891, 1995, also on Kogelnik'scoupled wave theory. H. Kogelnik, “Coupled Wave Theory for ThickHologram Gratings”, The Bell System Technical Journal, vol. 48, no. 9,1969.

Holographic elements 112 and 114 can be either reflective ortransmissive, as shown in FIGS. 3 and 4, or a combination of reflectiveand transmissive type. The type of the holographic element (reflectiveor transmissive) is defined by a correspondingexperimental/manufacturing recording geometry known to those skilled inthe art. These geometries yield better adjustments to the specificweapon, more convenient eye position and higher resolution andwavelength selectivity for a reflection hologram.

The transparent plate 130 with the reticle implemented on it isilluminated by the LED module 140 placed in the vicinity of the plate130. The LED module 140 comprises, at least, one low power LED (˜20 mAdriving current value) and can have a light conditioning optic. The LEDlight can be either Blue, Green or Red, or of any other suitable colorcomprising three LEDs that is appropriate for target aiming. For LEDs ofdifferent colors (e.g., Blue, Red and Green), a switch 150 isincorporated on the LED module that allows a shooter to switch betweenthree colors depending on the background scene. E.g., for brown-redbackgrounds (desert type scenery) Green illumination can be chosen. Forgreen backgrounds (grass, trees), Red illumination can be chosen, etc.Thus, substrate-guided holographic sight provides a better, improvedvisibility of the aiming reticle on various backgrounds as compared tothe systems known in the prior art. Preferably, an LED(s) withnarrow-band emission is used, ˜20-25 nm FWHM.

If more than one LED is used, multiplexed holograms are used as known bythose skilled in the art. Holograms are recorded with a larger anglebetween recording beams (preferably reflection holograms) to avoidcrosstalk between reticle images retrieved with different holograms. Thecondition of avoiding crosstalk is to satisfy the difference in anglesof beams diffracted on wrong holograms so they do not intersect in theimage area, as known by those skilled in the hologram multiplexing art.

FIG. 2 shows an example of the actual ray-trace for substrate-guidedholographic sight. The rays are traced from the position of theshooter's eye towards the reticle, field-of-view ˜1.2 deg. The reticlecan be placed on either side of the substrate-guided holographic sightsubstrate. For instance, on FIG. 2 it is placed on the same side as theviewing holographic element. For achieving a more compact packaging, itcan be placed on the side of the substrate which is opposite to the onewhere a viewing holographic element is placed.

A flat fold mirror can be placed in between the reticle 230 andholographic lens 214 to provide a better over-all compactness of theweapon sight.

FIG. 5 shows the image quality (geometrical spot size) for the ray-traceof FIG. 5. A rather substantial amount of spherical aberration isvisible on the spot diagram. For the design shown on FIG. 2, theholographic lens 214 is recorded with ray-tracing software using adivergent spherical wavefront and a collimated wavefront. Thesewavefronts are not shown on FIG. 2, instead, a resultant ray-tracethrough existing HOEs is shown.

To improve the image quality, a method is developed that comprisesrecording an intermediate holographic element in a ray-trace software(e.g., in Zemax® or in Code V®), so that a final holographic lens 214 isrecorded by a collimated wavefront and a wavefront generated by theintermediate holographic element. Such procedure offers such advantagesas it is more robust (always converges to a solution) and more flexible(i.e., applicable to a variety of holographic element design tasks)compared to a traditional analytical recursive technique proposed, e.g.,in [13—Ya. Amitai, A. Friesem, I. Shariv, ‘Planar Holographic OpticalDevice for Beam Expansion and Display’, U.S. Pat. No. 6,169,613 B1(2001)].

FIGS. 6 and 7 show wavefronts that are used for recording with ray-tracesoftware the HOE 214: FIG. 6—a collimated wavefront and FIG. 5—awavefront generated by an intermediate hologram 515. Coordinates of thetwo points that are used in recording hologram 515 with ray-tracesoftware are variables for the merit function that also includes surfacetilts and decenters as variables as well. Point 449 is a point source,surface 444 represents a paraxial surface that can be implemented inpractice, e.g., using a high-quality achromatic doublet of the samefocal length as the paraxial lens manufactured, e.g., by JML Optical;element 414 is a plane for recording of the hologram 214. Intermediatehologram 515 is recorded with ray-trace software using a point source550 and a point at infinity (not shown); ‘paraxial’ lens 545 represents,e.g., a high-quality achromatic doublet which is of the same focallength as the ‘paraxial’ lens. FIG. 8 shows spot diagram forsubstrate-guided holographic sight that includes hologram 214 recordedusing the described method.

A sight with a single reticle can further be improved with a dynamicoverlay image by replacing the reticle with a micro display 217, asshown in FIG. 9.

The described embodiments of the method for design and fabrication ofthe holographic optics for the weapon sight refer to methods andtechniques to make ‘master’ holograms. The ‘master’ holograms need to bereplicated. This can be done, e.g., using contact copying of volume(‘thick’) holographic optical elements by means of a single laser beamillumination, known by those skilled in the art, with roll-to-roll webprocess. A flexible film such as static cling vinyl as an index matchingmaterial can be used. The advantage of this material is that it willsuppress the recording of spurious holograms and will allow dry contactcopying.

Another important factor in copying is that the photopolymer materialrequires an absorption liner such as black polyester or orange dyedpolyester (available, e.g., from CPFilms) as a top liner to avoidrecording spurious holograms.

The foregoing it will be observed that numerous modifications andvariations can be effectuated without departing from the true spirit andscope of the novel concepts of the present inventions. It is to beunderstood that no limitation with respect to the specific embodimentillustrated or should be inferred. The disclosure is intended to coverby the appended claims all such modifications as fall within the scopeof the claims. All of the references that follow are incorporated byreference as if set forth fully herein.

1.-10. (canceled)
 11. An optical device comprising a light guide plate,two holograms secured to the light guide plate, a reticle ormicrodisplay placed on the light guide plate, a damped least squareoptimized intermediate holographic element, and at least one LED modulein the vicinity of the light guide plate.
 12. The optical device ofclaim 11 further comprising a diffuser.
 13. The optical device of claim11 wherein the light guide plate comprises glass, polycarbonate,acrylic, or mixtures thereof.
 14. The optical device of claim 11 whereinthe light guide plate comprises a thickness in the range of 3 to 6 mm.15. The optical device of claim 11 wherein the light guide platecomprises a unitary body or a body comprised of a plurality of bodies.16. The optical device of claim 11 wherein the light guide platecomprises a single material or a plurality of materials.
 17. The opticaldevice of claim 11 wherein the light guide plate comprises a reflectivecoating on at least one surface.
 18. The optical device of claim 11wherein the light guide plate comprises a tint.
 19. The optical deviceof claim 11 wherein the light guide plate comprises the two holograms ona same surface of the light guide plate or an opposite surface of thelight guide plate.
 20. The optical device of claim 11 wherein at leastone of the holograms comprises a holographic element having opticalpower.
 21. The optical device of claim 11 wherein one of the hologramscomprises a holographic lens and the second of the holograms comprises aholographic grating.
 22. The optical device of claim 11 wherein the twoholograms comprise Bragg holograms.
 23. The optical device of claim 11wherein the two holograms are recorded with lasers of at least threedifferent colors.
 24. The optical device of claim 11 wherein theholograms are either reflective or transmissive or a combinationthereof.
 25. The optical device of claim 11 wherein the at least one LEDcomprises three LEDs comprising Blue, Green, and Red lighting.
 26. Theoptical device of claim 11 comprising more than one LED and amultiplexed hologram.
 27. The optical device of claim 11 furthercomprising a mirror.
 28. The optical device of claim 11 wherein thereticle comprises an image of one color or multiple images of one ormultiple colors displayed simultaneously.
 29. The optical device ofclaim 11 wherein at least one hologram is recorded using a divergentspherical wavefront and a collimated wavefront or a collimated wavefrontand a wavefront generated by the damped least square optimizedintermediate holographic element.
 30. The optical device of claim 11comprising an optical sight, a holographic sight, or a weapon sight. 31.The optical device of claim 11 wherein at least one of the holograms islaminated onto a thin substrate that is attached to the light guideplate.
 32. The optical device of claim 11 wherein the thin substrate andthe light guide plate are substantially transparent.
 33. The opticaldevice of claim 11 wherein the light guide plate comprises a firsttransparent region spanning the surface of one of the holograms; asecond transparent region spanning a surface of the other hologram; athird transparent region spanning a surface opposite to that of thesecond transparent region corresponding to a field of view; and atransparent volume throughout the light guide plate wherein othersurfaces are opaque.
 34. The optical device of claim 11 wherein thereticle or microdisplay is placed on either side of the light guideplate.
 35. The optical device of claim 17 wherein the coating comprisessilver metal.
 36. The optical device of claim 11 wherein the LEDcomprises a light conditioning optic.
 37. The optical device of claim 11wherein a switch is incorporated on the LED to permit switching betweencolors of light.
 38. The optical device of claim 11 wherein the LEDcomprises a narrow-band emission in the range of about 20-25 nm FWHM.39. The optical device of claim 11 wherein the reticle or microdisplayis placed on a same side of the light guide plate as a hologram.
 40. Amethod of designing and recording a holographic optical element havingoptical power comprising using an intermediate hologram and aray-tracing technique with dampened least squares optimization, whichminimizes merit function and optimizes image quality.
 41. The method ofclaim 40 wherein a flexible film is used as an index matching material.42. The method of claim 41 wherein a flexible film comprises a staticcling vinyl material.
 43. The method of claim 40 further comprising theuse of an absorption liner comprising a black polyester or orange dyedpolyester material as a top liner.
 44. The method of claim 40 whereinthe holographic optical element is recorded with lasers of one or morecolors.
 45. The method of claim 40 wherein the intermediate hologram isrecorded by the ray-tracing technique and a final hologram is recordedby a collimated wavefront and a wavefront generated by the intermediatehologram.